Global and domestic demand for fossil fuels continues to rise despite price increases and other economic and geopolitical concerns. As such demand continues to rise, research and investigation into finding additional economically viable sources of fossil fuels correspondingly increases. Historically, many have recognized the vast quantities of energy stored in oil shale, coal and tar sand deposits, for example. However, these sources remain a difficult challenge in terms of economically competitive recovery. Canadian tar sands have shown that such efforts can be fruitful, although many challenges still remain, including environmental impact, product quality, and process time, among others.
Estimates of world-wide tar sands reserves generally exceed 5 trillion barrels of oil, depending on the estimating source. Regardless, these reserves represent a tremendous volume and remain a substantially untapped resource. Only Canada and Venezuela currently have significant amounts of commercial production of oil from tar sands. A large number of companies and investigators continue to study and test methods of recovering oil from such reserves. Methods of extraction have included open pit mining or strip mining followed by various extraction and separation techniques and underground in-situ methods.
Among tar sand resources, the bitumen and sand arrangement can vary from location to location. For example, Canadian tar sands are water-wetted, i.e. a water envelope around the sand, while U.S. tar sands (predominantly found in Utah) are hydrocarbon wetted. This often demands distinct extraction techniques to address these differences. Hot water extraction is currently the most common extraction process used, although a wide variety has been proposed in the literature and tested on small scale. In situ processes generally include steam injection, steam assisted gravity drainage, solvent injection, cold flow, vapor extraction, or flame front combustion (e.g. toe to heel burning). Unfortunately, current tar sand or oil sand processes require significant amounts of energy and water. High water usage, in particular, can be a critical limiting factor for these processes. As a general rule, these processes require several barrels of water per barrel of petroleum produced. This water is unsuitable for further usage and is deposited in huge drainage and settling ponds. Due to the makeup of this water, including sand particles and processing chemicals, the water is slow to evaporate and thus becomes an environmental problem. Thus, environmental impacts, such as water usage, inability to recycle or otherwise use such water, greenhouse gas emissions, habitat disturbance, and the like can make commercial exploitation of these resources difficult. Methods are needed that accomplish environmental stewardship, yet still provide high volume fuel output.
Below ground in-situ concepts emerged based on their ability to produce high volumes while avoiding the cost of mining. While the cost savings associated with avoiding mining can be achieved, the in-situ method requires heating a formation for a long period of time due to the extremely low permeability of undisturbed formations. Perhaps the most significant challenge for any in-situ process is the uncertainty and long term potential of water contamination that can occur with underground aquifers. In the case of Shell's ICP method which can be applied to tar sands, oil shale or other deposits, a “freeze wall” is used as a barrier to, in theory, keep separation between aquifers and an underground treatment area. Although this is possible, no long term analysis has proven for extended periods to guarantee the prevention of contamination. Without guarantees and with even fewer remedies should a freeze wall fail, other methods are desirable to address such environmental risks.
For this and other reasons, the need remains for methods and systems which can provide improved recovery of hydrocarbons from suitable water-containing hydrocarbonaceous materials, which have acceptable economics and avoid the drawbacks mentioned above.